The present invention relates to a door impact beam. More particularly, the present invention pertains to a door impact beam, that is, a reinforcement member provided in a vehicle door for ensuring a security of occupants against a side collision of the vehicle.
A door impact beam (i.e., door reinforcement member) is provided in a vehicle door in order to ensure a safety of occupants upon the side collision of the vehicle. For fulfillment demands to improve fuel efficiency by minimizing the weight of the vehicle, the door impact beam is made of aluminum alloy, particularly, the door impact beam is made of an extruded member of the 7000 series aluminum alloy (i.e., Alxe2x80x94Znxe2x80x94Mg series) whose principle ingredients are 0.2-2.5 percent of magnesium and 4.5-6.0 percent of zinc. The percentage of the proportion of the metal composition is represented as mass percent.
FIG. 5 shows a cross sectional view of a known door impact beam. A vehicle door impact beam 1 includes plate shaped flanges 2, 3, on top and bottom of FIG. 5 and a pair of webs 4, 5 for connecting the flanges 2, 3. Flange width W corresponds to 30-50 mm, a width from an external surface of the web 4 to an external surface of the web 5 corresponds to 15-25 mm, a plate thickness of flanges 2, 3, and webs 4, 5, corresponds to 2-3.5 mm, and a height from an external surface of the flange 2 to an external surface of the flange 3 corresponds to less than 32 mm.
Both ends of the door impact beam are supported by the door structure. When a load generated by the side collision is applied on the flanges 2, 3, the door impact beam bends. During the bending process, the cross-sectional form of the impact beam is maintained. Thus, the compression stress affects on the first flange to which the load is applied and the tensile stress affects on the second flange opposing to the first flange. By experiments and theoretical analysis, it is proven that a fracture of the impact beam occurs, when the tensile stress affecting on the second flange exceeds the critical stress, and absorbed amount of impact energy by the door impact beam is limited.
In order to improve an impact energy absorption characteristics, Japanese Patent Laid-Open Publication No. 5-330450 discloses a door impact beam configuration including a pair of separately disposed webs having different plate thickness each other. The door impact beam thus formed with unsymmetrical webs absorbs the side impact energy efficiently, because of large bending deformation, when the impact load is applied on the flange surface in rather exact perpendicular direction as expected by design. In this case, the webs are deformed to reduce the cross-sectional height and the increase of the tensile stress on the second flange is eased not to exceed the critical stress during the bending process. However, for the impact load in different from the expected direction by the design which makes the cross-section collapse, and the thin web is easily fractured, and falls to exert enough impact energy absorption function.
Japanese Patent publication No. 3103337 discloses a door impact beam which has bores on a flange and a web, in order to sift a neutral axis position (i.e., a balancing position of the tensile and compression stress) of section modulus of the door impact beam. The neutral axis position is shifted towards a direction of a flange to make the tensile stress reduced on the flange. Though the tensile stress is eased and the increased bend is permitted in this manner, the reduced section modulus by the bores renders the impact beam to be weakened for loads in directions deviated from the designed direction, also providing the bores on the flange and web boosts manufacturing cost.
A need thus exists for a door impact beam which prevents the fracture of the door impact beam while maintaining the larger section modulus.
In light of the foregoing, a door impact beam for a vehicle comprises a flange for receiving a load, a reinforcement body having a cross section providing with a pair of side portions connected with the flange and a bottom portion connected with the side portions via each curved portion, and the side portions being inclined in an outward direction to increase a width of each other while extending from the flange to the bottom portion.
According to another aspect of the present invention, a door impact beam for a vehicle comprises, a flange for receiving a load, a reinforcement body having a cross section providing with a pair of side portions connected with the flange and a bottom portion connected with the side portions via each curved portion, the side portions being inclined in an outward direction to increase a width of each other while extending from the flange to the bottom portion, and a neutral axis of a cross section modulus of the door impact beam being positioned approximately on a center of a height between the flange and the bottom portion.